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Unexpected reduction-allylic oxidation of hemisynthetic diosphenols from longipinene derivatives

Abstract:

The 7β,9α-dihydroxylongipin-2-en-1-one (1) was obtained by basic hydrolysis of a dichloromethane extract of the resinous exudate from aerial parts of Stevia lucida. The treatment of 1 with potassium permanganate in concentrated hydrochloric acid generated two diosphenolic derivatives (2 and 3) one of which showed an unexpected allylic oxidation (2). Diosphenol 3 was treated with Jones reagent yielding four oxidation products (4-7). Two of these (4 and 6) have structural changes that suggest a process of reduction of the enolic double bond of diosphenol and another process of allylic oxidation. To explain the formation of the compounds 4 and 6 a plausible reaction mechanism based on a sequence of isomerizations was proposed. The structures of (1-7) were established based on NMR (1D and 2D) data interpretation.